The present invention relates to saw blades, especially for sawing metals. Saw blades for sawing metals are made with teeth of a hard wear-resist material such as tungsten carbide or high-speed steel. Hardness is, however, usually accompanied by brittleness, and metal saw blades often fail by fracturing or chipping at the corners of the teeth, which are highly stressed in conventional saw blade configurations. For example, saw blades for metal sawing in a circular saw, bandsaw or hack saw machines are commonly made with carbide teeth for best wear resistance, the teeth being brazed in place, e.g., see U.S. Pat. No 4,784,033. The carbide teeth are somewhat wider than the steel part of the saw and have fully ground cutting edges. This method produces saws with excellent durability, but is somewhat costly since it involves numerous manufacturing steps and fairly large (thick) carbide pieces.
Saw blades for metal sawing have been proposed in which the teeth have the same thickness as the rest of the blade. At least some of the teeth are set right or left to cut a wider kerf than the blade thickness, thus minimizing friction and permitting passage of chips and coolant. Such blades can be made from a wide strip of spring steel onto the edge of which is welded a narrow strip of high-speed steel. Teeth are then formed in the edge of the narrow strip by grinding, milling or blanking, so that at least the tips of the teeth comprise high-speed steel. The teeth are set right and left by the actuation of mechanical hammers or plungers striking what is to be the inner corner of the tooth, causing local deformation, overstraining and reduced strength at that corner.
Another method to provide wear-resistant teeth with a thickness equal to the blade thickness involves welding small carbide spheres onto the teeth as described in U.S. Pat. No. 3,104,562, followed by grinding the top, sides and face of the teeth flush with the adjacent steel parts of the teeth, and then setting the teeth as described above. Because of the difficulty in choosing grinding parameters suitable for carbide as well as steel, the strength of the edge and corners is less than for edges where the grinding only touches the carbide, such as with welded or brazed teeth which are wider than the blade. The corners are further weakened by the setting, especially if the carbide tips are made wider than the blade.
The stresses in a corner of a tooth during sawing are moderate if the edge is in contact with the sawn material only on one side of the corner, or if the angle of the corner is obtuse. If the edge is in contact with the sawn material on both sides of the corner, the intersecting streams of chips will cause large fluctuating stresses in the corner, especially if the angle is acute. The worst case occurs if the edge on one side is in steady contact with the sawn material, and the edge on the other side is in intermittent contact with the sawn material.
For example, in one type of saw blade according to the prior art, a cross section of which is shown in FIG. 3, the teeth, prior to setting, are of equal height. Because of the tilting of the teeth associated with the setting, all corners of all teeth are exposed to cut the sawn material.
The inner corners 17 of the set teeth 11, 12, which were already weakened by the impact of the setting tool, are highly stressed because the edge is in contact with the sawn material on both sides of the corner, so the set teeth are easily damaged in use. The outer corners 18 are less stressed in use and are not weakened by setting. The vertical or side parts of the edges adjoining the corners 16 of the straight teeth 14 are in intermittent contact with the sawn material, causing large stresses and risk of damage.
Another saw blade according to the prior art, such as U.S. Pat. No. 105,261, is shown in section in FIG. 4 and has straight teeth 115 which are higher than the set teeth 111, 112. In this saw blade the inner corners of the set teeth are not exposed to cutting and are in no risk of damage, but the corners 119 of the straight teeth are very highly stressed especially when entering a cut. Even small damage to the straight teeth will impair the otherwise excellent ability of this blade to produce very straight and smooth cuts. When this blade design is used for a blade with welded-on teeth, it is a common occurrence that the attempt to grind the sides of the blade flat to remove the excess material from the welding will produce a slightly tapering blade where the tips are slightly narrower than the rest of the blade. That tapering will then produce extreme stresses in the straight teeth and require large cutting and feed forces.